Flotation hull



United States Patent C 3,139,635 FLOTATION HULL George H. Datfer,Shepherdstown, W. Va., assignor to Renaer, Inc, Williamsport, Md., acorporation of Maryland Filed July 5, 1962, Ser. No. 207,669 3 Claims.(Cl. 96)

This invention relates to improvements in generally light weight rigidflotation hulls particularly adapted for use in connection with seaplanes, amphibious aircraft and the like in which the hulls are filledwith and reinforced by a unicellular plastic foam adapted to prevent theentry of water into the hull in case of damage and thereby to eliminatethe necessity for providing excess buoyancy for flotation in case ofpartial flooding, as is necessary in hulls having hollow flotationcompartments.

The improvements relate both to such a hull and to an improved processof forming the same.

It has heretofore been known to provide a flotation hull in which thevarious compartments between the bulkheads or ribs have beensubstantially completely filled with a plastic unicellular foam eitherof the foam in place type or the type which is formed by being built-upfrom blocks or slabs of plastic foam material. In either event, however,it has been customary to apply the foam to a completed hull structure inwhich the various bulkheads or ribs and the skin of the hull have beenassembled as a unit prior to the placing of the plastic foam therein.Where the foam is then applied in the form of low density blocks ofplastic foam built-up to form the desired filling within the hull, suchlow density composite filling is incapable of supplying the desiredtoughness and rigidity immediately adjacent the skin of the hull andfurthermore, the process is not well adapted to mass production andassembly methods. On the other hand, where the flotation compartmentshave been completely filled with liquid foam plastic materials of anature resulting when cured in a unicellular plastic structure, it hasbeen quite difficult to fabricate such sections because of the largevolume and height to which the foam must rise. Accordingly, forproviding such foamed in place flotation compartment fillings it hasbeen necessary to use high density foams to achieve the desiredhomogeneity and strength with the result that it has not been foundpractical to achieve the degree of lightness of structure originallyhoped for.

With the foregoing in mind, one of the objects of the invention is toachieve a new strong and yet light flotation hull construction which isadapted to mass production and assembly methods and yet which willpermit the formation or disposition within the flotation compartments offillings or cores of unicellular plastic of comparatively low density,spaced somewhat from the hull, and in which the resulting spaces areoccupied by monolithic slabs of relatively higher density foam adaptedto be applied by foaming in place techniques.

It is a further object to provide such a flotation hull construction inwhich the rigid frame work such as may be comprised by the keel and theribs or bulkheads, may be preassembled as a unit together with the innercore structure for subsequent application to a separately formed skin orouter shell of the hull.

The novel process of forming the hull structure consists in forming aninner core of substantially uniform low density plastic foam blockshaving a rigid frame embedded therein, with portions of the frameprojecting outwardly from the foam body of the core; placing said corewithin a generally similarly shaped but larger hollow shellor skinadapted to engage the projecting frame portions, supporting the core inspaced relation from the sides and bottom of the shell by means of theseprojecting portions and then filling the spaces between the inner coreand the shell with a liquid or flowable composition for forming aunicellular plastic foam of greater density than that of the foam coresections. The flowable composition is then cured and bonded to the skinand the projecting portions of the rigid frame.

In order to facilitate the carrying out of the process, the hull shellor skin may advantageously be formed and supported within the cavity ofa suitable mold or jig structure and the inner core and frame may beassembled on and temporarily secured to a rigid supporting plate shapedand adapted to function as the top or cover for the mold cavity. Theresulting assemblage is formed with suitably disposed filler and ventopenings extending through the cover plate to facilitate the pouring ofthe flowable foam forming composition into the spaces or cavitiesbetween the low density foam and the hull shell and to permit theventing of air from such spaces.

In the accompanying drawings there is illustrated, for purposes ofexemplification, one form of flotation hull formed in accordance withthe invention and from which the process of the invention will be madereadily apparent in conjunction with the following more detaileddescription.

In the drawing:

FIGURE 1 is a side elevation of a flotation hull embodying the featuresof the invention and constructed in accordance with the process of thepresent invention, the broken line portion of this View illustratingfragmentarily the outline of a portion of an aircraft cabin which may besupported on the hull,

FIGURE 2 is a plan view of the hull shown in FIG- URE 1, prior toapplication of its deck,

FIGURE 3 is a cross section through the hull structure on the line 3-3of FIGURE 1,

FIGURE 4 is a cross section taken on the line 44 of FIGURE 1,

FIGURE 5 is a plan view of the mold cover plate having the combinedinner core and frame of the hull secured thereto for disposition withinthe outer skin or shell of the hull, and

FIGURE 6 is an enlarged fragmentary cross section on the same plane asFIGURE 3 illustrating fragmentarily a portion of the mold or jigstructure in which the outer skin or shell of the hull may be formed andsupported and also showing the association therewith of the mold coverplate and the inner core of the hull after the pouring of the relativelydenser outer sheathing or monolithic plastic foam sections betweenadjoining bulkheads has been completed,

Referring now in detail to the accompanying drawing, at firstconsidering the completed hull structure shown in FIGURES l and 2, itwill be noted that this structure comprises a unitary outer shell orskin 10 formed from a suitable material such as fiber glass reinforcedplastic, within which is disposed a rigid reinforcing frame exemplifiedby the-keel or keel member 12 extending within the hull along itslongitudinal line of symmetry and a plurality of relatively spacedtransverse bulkheads, each designated 14 suitably secured to the keelmember 12 at various points along its length. The aforesaid framestructure may be formed of any suitable rigid material having therequisite lightness and strength, as for instance a light weight metal,wood or the like.

The multiplicity of flotation compartments into which the interior ofthe hull is subdivided by the frame structures 12 and 14 and by theoverlying deck 16, are completely filled with unicellular plastic foamwhich, as shown in FIGURE 6, comprises as to each compartment, an innercore section 18 of comparatively low density and therefore lightweightunicellular plastic foam comprised of a series of united laminationssuch as 13A, 18B, 18C and 18D as best shown in FIGURE 4, with the innercore section in each compartment having its outer surface conformingroughly in shape to the adjoining interior of the hull shell or skin andspaced inwardly therefrom. Within the space thus provided there is amonolithic outer sheath section 2%) of a comparatively denser andtougher unicellular plastic foam which is preferably formed by pouringit into the space which it occupies and which is united both to theinner surface of the skin 10 and the projecting outer end portions ofthe several bulkheads 14, as well as to the outer surface portions ofthe inner core sections 18. The outer edges or profiles of therespective bulkheads which, as usual, conform accurately in shape anddimensions to the internal cross sections of the skin 10 are preferablycemented or bonded to the skin to increase the strength of the resultingstructure.

The deck 16 which may be of plastic, metal or other suitable material ispreferably applied and cemented or otherwise affixed in place as thefinal assembly step.

In the process of forming such a flotation hull, the outer skin or shell10 and the inner core or assembly, consisting of the frame members 12and 14 and the low density plastic sections 18 are separately formed.The inner core section is formed in inverted condition on an invertedmold cover plate 16 of rigid construction with its undersurfaceconforming in shape to the shape desired in the deck 16. In assemblingthese parts, the assembled frame, including the keel 12 and bulkheads14, is disposed in inverted relation on the inverted top plate or coverplate 16, the laminated and preformed foam sections 18 being disposedbetween the respective pairs of adjoining bulkheads and cemented both tothe bulkheads and the keel, but not being cemented to the top plate 16.

This assembled inner core structure or assembly is temporarily butfirmly secured to the undersurface of the cover plate 16 by means whichare exemplified by the slender bolts 22 respectively in the accompanyingdrawing, but which might equally well comprise wires or otherconventional temporary expedients.

The upwardly opening hollow shell or skin 10 in the meantime willpreferably have been disposed and rigidly supported within aconformingly shaped cavity, defined by an upwardly opening mold or jigfixture 24 shown fragmentarily in FIGURE 6. Before assembling theseparately formed structures, the foam sections 18 will respectivelyhave been formed with filler holes or openings 26 therethroughcommunicating with permanent filler openings 28 through the plate 16'.The plate 16 also has a series of permanent vent openings 30 disposedtherethrough adjacent its outer margin. The filler passages 26 and 28communicate with the lowermost portions of their respective compartmentsto deliver the flowable foam forming material between the low densityfoam l8 and the skin 10, while the air vents or vent openings 30respectively communicate with the uppermost portions of the spacesbetween the plastic sections 18 and the skin 10, whereby the risinglevel of the plastic foam poured through the interconnected passages 28and 26 will force the air completely out of the spaces through theirupper end vents 30. Where the several laminations of the respectiveplastic sections 18 are shaped by cutting or removing portions of theirouter surfaces, the roughened outer surface areas left by this cuttingoperation preferably are coated with a suitable adhesive composition 32,as indicated in FIGURE 6, prior to pouring of the high density foammaterial 20, so that after the pouring the ensuring curing of thismaterial to solid foam form will result in strongly securing theresulting monolithic slab or section 20 of foam to the inner coresection 18 therewithin, as well as to the skin 10 and the projectingportions of the keel 12 and the bulkheads 14.

It will be apparent that the portions of the frame members 12 and 14which project from the inner core structure into engagement with theskin 10 may be united to the skin by a suitable adhesive applied toeither or both of these parts prior to positioning the inner core withinthe skin and, if desired, also the entire inner surface of the skin mayhave been treated with a suitable cement or bonding agent to cause it tobe firmly and strongly united with the subsequently poured and curedfoam sheath sections 20. The frame structure thus defined, through itsprojecting portions will thus obviously serve to support the plasticinner core sections 18 in properly spaced relation from the skin 10during the operation of pouring the relatively denser sections 20. Also,the engagement between the mold top plate 16' and the skin will assistin this.

Following completion of the pouring and curing, the hull structure willbe substantially completed, except that it will be desirable to removethe comparatively heavy and rigid plate 16 by removing the nuts from theupper ends of bolts 22 and lifting off the plate 16. Preferably alighter permanent deck structure 16 of any suitable material such asWood, metal or fiber glass reinforced plastic, conforming in shape andconfiguration to the plate 16' is then substituted for plate 16. It willbe apparent that the plate 16 will have tended to confine the upperedges of the foam plastic sections 20 to the desired level determined byits under surface, except at the locations of the several openings 26and 30 at which points any projecting flash may be removed down to thelevel of the surrounding surface before application of the permanentdeck 16.

It will be obvious that if desired the mold cover plate 16' may beretained as the permanent deck of the resulting structure. Obviously theentire hull structure will have been completed and may be removed fromthe mold 24 after setting and curing of the foam plastic sections 20.The deck 16 may be applied either before or after removal of thestructure from the mold 24.

It will be apparent therefore that there has been described a novelstructure, including a relatively tough and high density foam sheathbetween the outer skin and an inner' core of relatively lower densityoccupying the greater internal volume of the hull.

The monolithic high density plastic sheath sections 20 interposedbetween the skin It) and the lower density plastic core sections 18, andunited to both, will obviously serve to greatly reinforce and strengthenthe resulting hull structure at the locations where reinforcement ismost desirable, while occupying but a comparatively small proportion ofthe total volume of the hull. The major portion of the volume will beoccupied by the relatively lower density inner core sections 18.

It will be readily apparent also that the invention comprises a newprocess of forming and assembling such a hull which process is welladapted for mass production of hulls in accordance with the invention.

Although the drawing and description in the present application aredirected only to the preferred embodiment of the invention, I am wellaware that the invention is capable of other and different embodimentsand that certain details of both the hull structure and the process offorming same are subject to modification without departing from theinvention. Because of this the accompanying drawings and description areintended to be merely illustrative in nature and not as limiting orrestricting the invention in any way other than as required by theexpress terms of the accompanying claims.

Having thus described my invention, I claim:

1. The process of forming a flotation hull comprising the steps offorming an inner core of substantially uniform low-density plastic foamhaving a rigid frame embedded therein, comprising the steps of embeddingportions of said frame in said low density plastic foam, while causingother portions of said frame to project from said plastic foam, placingsaid core and frame within a hollow hull shell, supporting said core inspaced relation from the sides and bottom of the shell by means of saidprojecting frame portions, fixedly securing said projecting frameportions to the shell by filling all space between the inner core andsaid shell with a flowable composition for forming a unicellular plasticfoam of greater density than said foam of the inner core, cun'ng saidflowable composition to solidify the foam formed thereby, and bondingsaid last mentioned foam to said inner core, said shell and saidprojecting portions of the rigid frame.

2. The process of forming a flotation hull comprising the steps offorming a sheet material skin to the desired external configuration ofthe hull, supporting said skin in an upperwardly opening mold cavity ofsimilar configuration to the skin, securing to a rigid mold cover platean inverted rigid open frame identical in overall configuration anddimensions with the interior of said skin, and including a plurality ofrelatively longitudinally spaced transverse rigid bulkheads havingprofiles respectively similar to the cross sections of the skin interiorat corresponding longitudinal locations, disposing in the spaces betweenadjacent bulkheads inner core sections each comprised of a unicellularlaminated plastic foam of comparatively low density, and adhesivelysecuring each said core section to said frame to form a composite frameand foam inner core structure in which the sides and bottom surfaces ofthe plastic foam sections are made to conform roughly to thecorresponding inner surface areas of the skin but are spaced inwardlyfrom the profiles of the sides and bottoms of said bulkheads, disposingsaid cover plate in operative relation over the mold cavity with saidinner core received within the skin and with the bulkheads engaging saidskin and supporting the plastic core sections in spaced relationtherefrom to define between the skin and said sections a series ofcavities of predetermined proportions and conformations, and fixedlysecuring said frame to the skin by pouring into said cavities a liquidcomposition for forming a unicellular plastic foam of greater densitythan said foam core sections, curing said compositions and bonding sameto said core sections, said skin and the exposed portions of said frame.

3. A flotation hull structure comprising an inner core of low densityunicellular plastic foam having a rigid frame imbedded therein, withportions of the frame projecting outwardly from said core, a sheetmaterial shell defining an upwardly opening cavity receiving said core,said projecting frame portions supporting said core Within the cavity inspaced relation from the sides and bottom of said shell, and beingunited at their areas of contact to the said shell, and unicellularplastic foam of greater density than said foam of the inner coreinterposed between said inner core foam and the skin and united to both,said greater density foam affording a sheath of relatively denser andtougher material than the inner core foam between the latter and theshell.

References Cited in the file of this patent UNITED STATES PATENTS1,368,935 Janecek Feb. 15, 1921 2,417,508 Leyde Mar. 18, 1947 2,653,139Sterling Sept. 22, 1953 2,716,246 Billingham Aug. 30, 1955 2,780,350Simon et al. Feb. 5, 1957 2,863,797 Meyer Dec. 9, 1958 2,866,985Blackmore Jan. 6, 1959 3,007,208 Urban Nov. 7, 1961 3,013,922 FisherDec. 19, 1961 3,070,817 Kohrn et al. Jan. 1, 1963 FOREIGN PATENTS1,220,409 France Jan. 4, 1960

3. A FLOTATION HULL STRUCTURE COMPRISING AN INNER CORE OF LOW DENSITYUNICELLULAR PLASTIC FOAM HAVING A RIGID FRAME INBEDDED THEREIN, WITHPORTIONS OF THE FRAME PROJECTING OUTWARDLY FROM SAID CORE, A SHEETMATERIAL SHELL DEFINING AN UPWARDLY OPENING CAVITY RECEIVING SAID CORE,SAID PROJECTING FRAME PORTIONS SUPPORTING SAID CORE WITHIN THE CAVITY INSPACED RELATION FROM THE SIDES AND BOTTOM OF SAID SHELL, AND BEINGUNITED AT THEIR AREAS OF CONTACT TO THE SAID SHELL, AND UNICELLULARPLASTIC FOAM OF GREATER DENSITY THAN SAID FOAM OF THE INNER COREINTERPOSED BETWEEN SAID INNER CORE FOAM AND THE SKIN AND UNITED TO BOTH,SAID GREATER DENSITY FOAM AFFORDING A SHEATH OF RELATIVELY DENSER ANDTOUGHER MATERIAL THAN THE INNER CORE FOAM BETWEEN THE LATTER AND THESHELL.